I think I had implantation bleeding 5-6 days after I had sex with my boyfriend. My period is not due for a week or more island what it is and I never have irregular periods off or on birth control I had heavy bleeding the first day first w brown discharge second day spotted by the third day nothing.. usually my period is 7 days... And a couple days after"" implantation "I am cramping w back aches side aches sometimes and it's around the time I would start what do I expect? Has this happened to anyone before is it implantation?!!